1. Field of the Invention
The present invention relates to surgical devices and methods for repairing tissue tears and, more particularly, to a device and method for repairing a meniscal tear in a knee.
2. Description of Related Art
The menisci of the knee are C-shaped disks of cartilaginous tissue interposed between the condyles of the tibia and the femur. They are actually extensions of the tibia that serve to deepen the articular surfaces of the tibial plateau to accommodate better the condyles of the femur (see FIG. 1). The material of the menisci is collagenous, and the fibers are oriented generally circumferentially.
As the menisci were long considered functionless remains of leg muscle, injury to this tissue had been treated by their total removal, called meniscectomy. A better understanding of these structures, combined with improvements in arthroscopic surgical techniques, has led to the development of meniscal repair techniques.
Posterior peripheral tears of the menisci may be treated by an open technique, wherein sutures are placed along the tear. An arthroscopic technique may also comprise placing sutures along the tear, but in this method through a cannula.
There are a number of fastener-type devices that are known in the art. A surgical fastener is disclosed by Screiber (U.S. Pat. No. 4,873,976) that comprises a shaft having at least one barb for locking the shaft in place when inserted into soft tissue. Also described is an applicator consisting of a cylinder into which the fastener is placed and out of which the fastener is pushed when positioned at the tear site.
Bays et al. (U.S. Pat. Nos. 4,884,572 and 4,895,148) describe a surgical-repair tack and applicator and method of using them. The tack has a barb member and is made of biodegradable material having a degradation time selected to coincide with the healing time of the tissue. In an alternate embodiment, the tack""s barb comprises a continuous helical barb.
The method and apparatus for repairing a meniscal tear disclosed by Winters (U.S. Pat. No. 5,059,206) comprises a fastener having protrusions or barbs that is applied to a meniscal tear with a delivery device. The delivery device has a flexible tip that is manipulable through a curved radius to enable the surgeon to insert the device into the central part of the knee and then extend the fastener radially outward into and across a meniscal tear.
A fastener, driving device, and method have been described by Justin and Winters (U.S. Pat. Nos. 5,569,252 and 5,xxx,xxx) wherein the fastener has a helical protrusion that is advanced across a tear in a screwing motion. In the latter patent, the protrusion has a variable-pitch for bringing two sides of the tear into apposition as the fastener is advanced across the tear. The fastener material preferably is a bioabsorbable, biocompatible, nontoxic plastic that is specifically designed to bioabsorb generally within the time span of the healing process. A delivery device for introducing the fastener was also provided that includes an elongated needle rotationally coupled with the fastener.
Stone et al. (Clin. Orthopaed. Rel. Res., No. 252, March 1990) introduced a resorbable collagen template for induced meniscal regeneration.
No method of repairing meniscal tissue with a device made from a core of bioabsorbable material and outer tubes or bands of expanding collagen is known to have been disclosed, however.
It is an object of the present invention to provide a bioabsorbable fastener and method for repairing a tear in soft tissue.
It is a further object to provide such a fastener that is made from a nontoxic, biocompatible, bioabsorbable material.
It is an additional object to provide such a fastener having a shape designed to compress the tear.
It is another object to provide such a fastener shaped to resist forces tending to pull apart the tear during the healing process.
It is yet a further object to provide such a fastener that expands following introduction across the tear.
These and other objects are attained with the fastener and method of the present invention. The fastener of the present invention is designed for repairing a tear in soft tissue of a patient, a particular exemplary embodiment comprising a meniscal tear in a knee.
The fastener in a first embodiment comprises an elongated core that has a distal portion that has a narrowing cross section toward a pointed distal end. Such a shape is for facilitating an insertion of the fastener into soft tissue. The core also has a narrowed central portion that extends between the proximal end and the distal portion.
The fastener additionally comprises a collagen band that is positioned in surrounding relation to the core""s central portion. The collagen band is expandable between a dehydrated state for insertion and a hydrated state for healing. This collagen band is preferably shaped to bring two opposing sides of the tear into apposition, which promotes healing. The swelling caused by hydration creates an interference fit between the fastener and the soft tissue, which retains the fastener in position and resists a force tending to remove it therefrom.
In a preferred embodiment, the core material comprises a material that is biocompatible with the soft tissue of the patient and has a rigidity sufficient to support movement. The polymer core material is specifically designed to be biodegradable within a first time span greater than or equal to a second time span over which the sides of the tear can knit together. This feature permits the fastener to remain in place for as long as required for the tear to heal, but ultimately to be bioabsorbed and be dissipated harmlessly into the patient""s system.
Alternatively, the core material comprises suture material that is bioresorbable.
In another embodiment the fastener comprises a unitary material, such as only rigid polymer or only collagen, and has means at the distal and proximal ends for holding the two sides of the tear in apposition. Such means may comprise barb-shaped protrusions or split sections that are biased to flare open when not under tension.
The method of the present invention is for repairing a tear in soft tissue of a patient. The method comprises the steps of driving a trocar across the tear in a direction generally normal to the tear and passing a tube over the trocar to a position wherein the tube breaches the tear. Next the trocar is removed from the soft tissue. A fastener containing collagen, or some other expandable polymer, such as described above in a dehydrated state is then introduced into the tube and pushed to a position adjacent a distal end of the tube. Next the tube is removed from the soft tissue, leaving the fastener in position to breach the tear.
The fastener is permitted to hydrate in situ, which causes the collagen band to swell, bringing the opposing sides of the tear into apposition and forming an interference fit between the fastener and the soft tissue. As described above, this serves to retain the fastener in position.
In one of the embodiments of the fastener described above, which comprises a rigid polymer without collagen, after positioning, the shape of the fastener holds the two sides of the tear together.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.